After you have Outlook 2013 setup, open the "old" pst file in Outlook 2013 and then you can "copy and paste" or select some items, right click, and "move". When you are finished just close the "old" file.

I am totally agree with Joe suggestion, but somewhere copy and paste can create some duplicate items in your current Outlook Data File.
Rather than going for “copy and paste” option, you should prefer “Import and Export” wizard because using this method you can also apply to filter for the duplicate items.

Here is a cheat-sheet I wrote for an old version of Outlook. The process still works as I have done it for my Outlook 2007 & 2010 updates but some of the locations of the necessary options have changed so look them up and note the changes before starting. Of course you can ignore the part about Dual-Boot, i.e. you only need to do it once. FYI I keep my .PST files in an Outlook folder under Documents so it gets backed up w/rest of my docs. (I can't remember if MS has changed the default location to Documents but it didn't used to be there!) HTH